Pm

Promethium

Identification

CAS Number: 7440-12-2

Discovery Year: 1945

Discoverer: J.A. Marinsky, L.E. Glendenin, C.D. Coryell

Discovery Location: United States

Properties

Atomic Mass: 144.91276 →Density: 7.26 g/cm³ →

Atomic Dimensions

Atomic Radius: 185 pm →

Atomic Radius (Rahm): 283 pm

Covalent Radius: 199 pm →

Van der Waals Radius: 238 pm

Thermodynamics

Melting Point: 1441 K →Boiling Point: 3000 K →Specific Heat: 0.185 J/(g·K) →Thermal Conductivity: 17.9 W/(m·K) →

Electronic Structure

Electron Config: [Xe] 4f5 6s2

Block: f

Period: 6 →

Oxidation States: +3

Abundance & Geochemistry

Geochemical Class: rare earth & related

Goldschmidt Class: litophile

About

Soft silvery metallic element, belongs to the lanthanoids. Pm-147, the only natural isotope, is radioactive and has a half-life of 252 years. Eighteen radioisotopes have been produced, but all have very short half-lives. Found only in nuclear decay waste. Pm-147 is of interest as a beta-decay source, however Pm-146 and Pm-148 have to be removed from it first, as they generate gamma radiation. Discovered by J.A. Marinsky, L.E. Glendenin and C.D. Coryell in 1947.

Isotopes

Pm-145 145 ☢ 17.7 s

Pm-146 146 ☢ 5.53 a

Pm-147 147 ☢ 2.62 a